1. Field of the Invention
The present invention relates to a method for controlling a compression ignition internal combustion engine.
2. Description of the Related Art
In recent years, for reducing a fuel consumption per predetermined load or per predetermined time in an internal combustion engine, a compression ignition internal combustion engine represented by a premix compression ignition internal combustion engine has been under consideration. For the compression ignition internal combustion engine, however, it is difficult to control timing of ignition unlike a spark ignition internal combustion engine. Furthermore, the compression ignition internal combustion engine has a problem such that knocking easily occurs when a demand load of the engine increases if a fuel of high ignitability is used, while misfire easily occurs when the demand load decreases if a fuel of low ignitability is used, thus narrowing the operation range.
For solving the problem, a technique has been known in which a fuel of high ignitability and a fuel of low ignitability are provided, and both the fuels are mixed and supplied to the engine (e.g. see Japanese Patent Laid-Open No. 2001-355471). According to the technique, the mixing ratio of the fuels is adjusted in accordance with the demand load of the compression ignition internal combustion engine, whereby the engine can be stably operated for a wide range of demand loads. In the technique, however, the fuel of high ignitability and the fuel of low ignitability are separately stored, and therefore a plurality of tanks are required.
On the other hand, a technique is also known in which a single fuel is used, and part of the fuel is partially oxidized to produce an ignitability controlling material when the demand load of the compression ignition internal combustion engine increases (e.g. see Japanese Patent Laid-Open No. 2000-213444). Specifically, the technique is such that part of a hydrocarbon based fuel such as light oil is partially oxidized to produce an ignitability controlling material such as formaldehyde, and has an advantage that only one fuel tank is required.
However, the technique has a disadvantage that a high-temperature and long-time reaction is required for partially oxidizing the hydrocarbon such as light oil to produce formaldehyde.